Backflow is an undesirable reversal of water flow or other liquids into the public water supply or a private plumbing system. This phenomenon is typically caused by changes in water pressure. For instance, if there is a water main break, a decrease in pressure can force water back into the pipes, contaminating the clean water supply.
Types of Backflow
There are two primary types of backflow:
Backsiphonage
Backsiphonage occurs when the pressure in a plumbing system is reduced, causing water to be sucked back into the plumbing.
Backpressure
Backpressure happens when the pressure in a plumbing system exceeds that of the public water supply, resulting in water flowing backward.
Why Is Backflow a Problem?
Backflow can contaminate drinking water with harmful substances, such as sewage, pesticides, or chemicals. These contaminants pose serious health risks, making it essential to prevent backflow in plumbing systems. Installing the right backflow prevention devices is crucial to mitigate these risks.
Plumbing Devices That Prevent Backflow
Backflow Preventer Valve (BPV)
One of the most common devices used to prevent backflow is the backflow preventer valve. This valve automatically shuts off water flow if it detects reverse flow. The backflow preventer valve typically consists of two main components: check valves and shut-off valves.
How It Works
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The valve allows water to flow in one direction—toward your home or facility.
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If backflow occurs, the valve automatically shuts off the water flow, preventing contaminants from entering your plumbing system.
Types of Backflow Preventer Valves
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Double Check Valve Assembly (DCVA): This type of backflow preventer features two check valves that work together to stop water from flowing backward.
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Reduced Pressure Zone (RPZ) Valve: The RPZ valve is more advanced and provides greater protection. It includes a pressure relief valve that prevents backflow even under high-pressure conditions.
Check Valve
A check valve is a mechanical device that ensures water flows in a single direction. It can be installed at various points within a plumbing system, including the main water line and irrigation connections.
How It Works
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The check valve consists of a flap or disc that opens when water flows in the correct direction.
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If reverse flow occurs, the flap or disc closes, preventing backflow and contamination.
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Check valves are often used alongside other backflow prevention devices for added protection in sensitive areas of the plumbing system.
Pressure Vacuum Breaker (PVB)
A pressure vacuum breaker is a backflow prevention device typically installed in irrigation or outdoor plumbing systems. It is commonly found in both residential and commercial buildings.
How It Works
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The PVB includes a valve that opens when water pressure is normal, allowing water to flow freely.
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If there is a sudden loss of pressure, such as during a water main break, the vacuum breaker opens, allowing air into the system. This breaks the vacuum and eliminates backflow.
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Plumbing codes often require PVBs in irrigation systems to prevent contamination of the potable water supply.
Atmospheric Vacuum Breaker (AVB)
An atmospheric vacuum breaker is a simple device used in residential plumbing systems to prevent backsiphonage. It is often used in sprinkler systems or on hose-attached faucets.
How It Works
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The AVB is installed at the top of the plumbing system or hose connection.
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When water pressure decreases, the atmospheric vacuum breaker opens, allowing air into the system and preventing reverse flow that could pollute the water.
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While effective in most situations, the AVB is not suitable for high-pressure systems and does not address backpressure.
Hydraulic Control Valves
In more complex plumbing systems, such as those found in commercial or industrial applications, hydraulic control valves can be utilized to regulate water pressure and ensure proper water flow direction.
How It Works
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These valves automatically control water flow to maintain desired pressure levels and prevent backflow.
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They can be programmed to detect pressure changes and adjust water flow accordingly.
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Hydraulic control valves are ideal for preventing both backsiphonage and backpressure in systems requiring precise water control.
Choosing the Right Backflow Prevention Device
Selecting the appropriate backflow prevention device depends on several factors, including the type of plumbing system, the risk of contamination, and local plumbing codes.
Considerations for Selection
Plumbing System Type
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Residential: In most residential plumbing systems, common devices include check valves, PVBs, and AVBs to prevent backflow.
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Commercial/Industrial: Larger, more complex systems may require devices like RPZ valves or hydraulic control valves for effective backflow protection.
Risk of Contamination
Backflow preventers are essential for protecting the potable water supply, especially if your plumbing system connects to an irrigation system, pool, or any system that uses chemicals or fertilizers.
Local Plumbing Codes
Consulting local plumbing codes is advisable, as many municipalities have specific requirements regarding backflow prevention devices. These codes often mandate the installation of certain devices based on contamination risk.
Conclusion
In conclusion, backflow in plumbing poses significant risks to public health and safety. Understanding the types of backflow and the devices available to prevent it is crucial for maintaining a safe water supply. By selecting the appropriate backflow prevention devices and adhering to local plumbing codes, you can protect your plumbing system and ensure the safety of your drinking water.
For more information on backflow prevention devices, visit this link.
